|author||Grant Likely <email@example.com>||2011-04-28 14:27:23 -0600|
|committer||Grant Likely <firstname.lastname@example.org>||2011-05-23 09:30:20 -0600|
dt: add documentation of ARM dt boot interface
v6: typo fixes v5: clarified that dtb should be aligned on a 64 bit boundary in RAM. v3: added details to Documentation/arm/Booting Acked-by: Tony Lindgren <email@example.com> Acked-by: Nicolas Pitre <firstname.lastname@example.org> Acked-by: Russell King <email@example.com> Signed-off-by: Grant Likely <firstname.lastname@example.org>
Diffstat (limited to 'Documentation/arm')
1 files changed, 29 insertions, 4 deletions
diff --git a/Documentation/arm/Booting b/Documentation/arm/Booting
index 76850295af8..4e686a2ed91 100644
@@ -65,13 +65,19 @@ looks at the connected hardware is beyond the scope of this document.
The boot loader must ultimately be able to provide a MACH_TYPE_xxx
value to the kernel. (see linux/arch/arm/tools/mach-types).
-4. Setup the kernel tagged list
+4. Setup boot data
Existing boot loaders: OPTIONAL, HIGHLY RECOMMENDED
New boot loaders: MANDATORY
+The boot loader must provide either a tagged list or a dtb image for
+passing configuration data to the kernel. The physical address of the
+boot data is passed to the kernel in register r2.
+4a. Setup the kernel tagged list
The boot loader must create and initialise the kernel tagged list.
A valid tagged list starts with ATAG_CORE and ends with ATAG_NONE.
The ATAG_CORE tag may or may not be empty. An empty ATAG_CORE tag
@@ -101,6 +107,24 @@ The tagged list must be placed in a region of memory where neither
the kernel decompressor nor initrd 'bootp' program will overwrite
it. The recommended placement is in the first 16KiB of RAM.
+4b. Setup the device tree
+The boot loader must load a device tree image (dtb) into system ram
+at a 64bit aligned address and initialize it with the boot data. The
+dtb format is documented in Documentation/devicetree/booting-without-of.txt.
+The kernel will look for the dtb magic value of 0xd00dfeed at the dtb
+physical address to determine if a dtb has been passed instead of a
+The boot loader must pass at a minimum the size and location of the
+system memory, and the root filesystem location. The dtb must be
+placed in a region of memory where the kernel decompressor will not
+overwrite it. The recommended placement is in the first 16KiB of RAM
+with the caveat that it may not be located at physical address 0 since
+the kernel interprets a value of 0 in r2 to mean neither a tagged list
+nor a dtb were passed.
5. Calling the kernel image
@@ -125,7 +149,8 @@ In either case, the following conditions must be met:
- CPU register settings
r0 = 0,
r1 = machine type number discovered in (3) above.
- r2 = physical address of tagged list in system RAM.
+ r2 = physical address of tagged list in system RAM, or
+ physical address of device tree block (dtb) in system RAM
- CPU mode
All forms of interrupts must be disabled (IRQs and FIQs)